This commit improves the handling of default_url_options in integration
tests by making behave closer to how a real application operates.
Specifically the following issues have been addressed:
* Options specified in routes.rb are used (fixes #546)
* Options specified in controllers are used
* Request parameters are recalled correctly
* Tests can override default_url_options directly

A callable object passed as a constraint for a route may access the request
parameters as part of its check. This causes the combined parameters hash
to be cached in the environment hash. If the constraint fails then any subsequent
access of the request parameters will be against that stale hash.
To fix this we delete the cache after every call to `matches?`. This may have a
negative performance impact if the contraint wraps a large number of routes as the
parameters hash is built by merging GET, POST and path parameters.
Fixes #2510.
(cherry picked from commit 5603050)

Make sure to return the same hash object instead of returning a new one.
Returning a new one causes failures on cookie store tests, where it
tests for the 'Set-Cookie' header with the session signature.
This is due to the hash ordering changes on Ruby 1.8.7-p358.